Just This Once
by winter machine
Summary: My first attempt at MerDer. A post-episode one-shot for "Yesterday," in which life does actually come down on the side of the dirty mistresses. Told from Meredith's perspective. Meredith/Derek, Addison/Mark.


**Author's Note:** Baby's first MerDer, so I'm starting with something I know: Season 2, and specifically _Yesterday._ Beginning dialogue comes straight from the episode, everything belongs to Shonda except the happy ending. That episode, as you all know, ended with Meredith and Mark at Joe's while an unhappy Addison and Derek moped (separately) in the trailer. So let's change it up.

This is for Patsy and mandyg67, both of whom encouraged me to write MerDer after I got my feet wet with _When I Grow Up_ , so if you don't like the story, blame them. (Kidding. Blame me.) I'm sure this has been done before, and better, but a girl's got to start somewhere. So if you do like it ... I hope you'll let me know.

* * *

 **Just This Once**

" _What if you're wrong? What if, just this once, life comes down on the side of the dirty mistresses?"  
_ -Mark Sloan, _Yesterday_ (2.18)

...

"She won't show, you know?"

"No?" He doesn't look at her, just stares straight ahead, shoulders hunched in his leather jacket. Glasses clink around them; it smells like stale alcohol and damp wood in here.

"He's … not the kind of guy you leave if you can help it."

Mark sighs. "What if you're wrong? What if, just this once, life comes down on the side of the dirty mistresses?"

Meredith looks away for a moment.

"Life doesn't come down on the side of the dirty mistresses," she says finally. "That's what makes us dirty mistresses."

Mark orders another round. Double scotch, single malt.

"Tell me something," she begins, and he glances at her. "You order his drink. You sleep with his wife. You're here in Seattle. Are you sure _he's_ not the one you want?"

Mark looks amused rather than offended. "Who says Derek's not the one ordering _my_ drink?"

"Is he?"

"Nah. It's his drink. What can I say? He has good taste. … in many things," he adds with a smirk.

"Don't do that. Don't flirt with me."

"Who's flirting?"

"You're flirting. Don't. That's not what dirty mistresses do."

"That's exactly what dirty mistresses do."

"Right. But they don't flirt with each other, they flirt with …"

"Married guys," Mark offers helpfully.

" _And_ married women," she counters.

Long moments, and an another round, pass.

Mark turns toward the door each time the chimes jingle. He still hasn't given up hope; Meredith can't decide if it's touching or pathetic.

There's actual hurt in his eyes when he turns around this time.

"You want another?" His voice is duller now, the teasing tone gone.

"I probably shouldn't. I'm working tomorrow."

"And I'm flying tomorrow."

The chimes jingle again. "Mark…" Meredith touches his arm before he can turn around. "Don't do that."

"Do what? Hope?"

"Well, yeah."

"Just because you've given up…"

"She's not going to show," Meredith reminds him gently.

"She might show," he mutters into one more shot.

"She's not going to."

"She _might_ ," he insists.

"She might, but she probably doesn't expect to find you drinking with Meredith Grey."

They both turn around to see the woman, looking slightly worse for the wear, standing a few feet away from them. Her eyes are puffy, her hair actually disheveled – _Satan can cry_ , that's her first uncharitable thought, but whatever she did tonight clearly put her through the wringer.

"Addison," Mark croaks.

This should be Meredith's cue to leave, except if Addison's _here_ , then that means…

"Mark wasn't drinking with me," she hastens to explain. "I mean, he was drinking with me, but he wasn't drinking _with_ me…" her voice trails off. "He's still in love with you, you know."

" _Meredith_." Mark glares at her over the rim of his glass.

"It's okay. I did know that, already." Addison sighs, and she and Mark exchange a long look.

"You, uh, you want a drink?" Mark asks finally, nodding toward the bar.

"No, thank you. I'm the only one of us sober enough to drive."

"Where are we driving?" Mark looks confused.

"Back to the trailer."

"Is this some kind of joke? You drive out here and then I have to watch you go back to Derek again?"

"Mark. You don't get it." She rests a hand on his shoulder, tentatively, like she's afraid to hurt him, Meredith thinks. "I'm not going back to Derek. _She's_ going back to Derek."

"I'm sorry?" Meredith looks from Addison to Mark.

"She's still in love with him," Mark says to Addison, and she nods.

"This is getting too weird, even for me. I think I'll just … well, good luck with everything, Mark, and Addison, I mean Dr. Shepherd, I'll, uh, see you at work." She reaches for her coat.

From Derek to Addison to Mark, every single person who flies to Seattle from New York seems to have a screw loose.

She's halfway to the door when a voice stops her.

"He's in love with you, Meredith."

Hating herself just a little, she turns around. "He is?"

Addison nods. "He told me."

Out of the corner of her eye, Meredith sees Mark shaking his head, looking somewhere between dumbfounded and impressed.

"He told you," Meredith repeats blankly. "He told … _you_ , that he's in love with me?"

Addison gestures at the stool next to Mark's and, sighing slightly, Meredith climbs back onto it. She doesn't take her coat off, though. She has _some_ pride.

"He told me he's in love with you," Addison says again. "Right here, in fact," and she gestures toward a table in the corner.

"In a bar."

"In a bar," Addison confirms. "This bar."

"This bar is where we met," Meredith admits. She doesn't want her voice to soften, remembering that night, but it does anyway.

"Why did he tell _you_ that he was in love with me?"

"I don't know." Addison looks sad for a moment, and then Meredith sees one of Mark's big, leather encased arms wrap around her waist, steadying her. That seems to help. "I … think he would say he was just trying to be honest."

"What would you say?"

"I'd say that he was trying to hurt me," Addison shrugs. "But … I think the truth is probably halfway in between."

"The truth?"

"You know – three sides to every argument, his side, her side, and the truth?" Addison smiles ruefully. "If I know Derek, and I think I do, even after … well, if I know Derek, then he might have just figured it out, and … he won't know this but he was giving me what I needed to leave."

"But you didn't leave," Meredith prompts. Mark slides another shot towards her and she drains it .

"No. I'm … an optimist, I guess."

"No, you're not." Mark looks confused.

"You're right, I'm not an optimist." Addison sighs. "We … weren't honest with each other, Derek and I. Since I've been here, I mean, and … well, that was on me, first," and she and Mark exchange a look Meredith doesn't understand. "But he … was in love with you, Meredith."

"Everyone loves a dirty mistress." Meredith sighs.

"Not as a dirty mistress, as a … look, can you just let me drive you over there?"

"You just drove all the way here," she points out.

"That's true." Addison nods. "And I just threw my eleven-year marriage down the drain and I just emailed one of my favorite people to break a very lucrative employment contract and I _just_ bought a ticket to JFK for tomorrow so … driving you back to the trailer isn't going to be the weirdest thing I did tonight."

Meredith doesn't miss the way Mark looks at her when she says _JFK._

Addison starts toward the door, then holds out her hand, much the way Meredith remembers doing at Derek's trailer the night he decidedly did _not_ tell her he was married. She doesn't take the outstretched hand.

"Mark – are you coming?" Addison props a hand on her hip.

"I don't think Derek will take it very well if I show up at his trailer with you," Mark says, fingering the bandaged slash on his cheek.

"We're not _showing up_ ," Addison says patiently. "We're driving Meredith, and then we're driving away. Together," she adds.

Meredith sees hope flickering on Mark's face. "Together?"

"Together."

Mark stands up. "Grey. Let's go."

"You're on her side now?"

"I've always been on her side," he says, and Meredith sees Addison's face soften. Those two really need to get a room, and the sooner the better, as far as she's concerned.

"Meredith … " Mark studies her for a moment. "If you love someone, you should tell them."

"What do you mean? I don't…" her voice trails off.

"Yeah, you do."

She stands up, slightly wobbly, and two different hands catch her, one under each elbow.

"How drunk are you?" Addison asks nervously.

"I metabolize quickly." Meredith shrugs while Addison orders a few bottles of water to go.

...

The ride back out to Derek's trailer is not short, and it's not _normal_ , let's face it. It might actually be the weirdest drive Meredith can remember as she stretches out in the backseat of Addison's fancy car that still smells like new leather, passing headlights swirling across her vision.

And Meredith still remembers waking up half-dressed on the back of a tractor in a field in … France, it was France, she's pretty sure, based on what the outraged man who found them was yelling. Yelling at her and at Jean, who was pantsless and drunk enough not to notice how sharp the hay was. And she was pretty sure she'd woken up in Spain that day. And that she didn't know how to farm. And that they were really, really far from civilization. Oh, and she didn't speak a word of French.

Still, though, _this_ is the weirdest car ride she's been on.

Because, let's face it, your perfect ex-boyfriend's perfect ex-wife and his – okay, a little dark and a little flirty but still pretty perfect – ex-best friend delivering you like a bouquet of flowers to the McTrailer you've had to try to forget … that's weirder.

She knows this route. She drove it not that long ago, with reinforcements, to drop Doc off at the trailer. And she watched Addison fuss over the dog and felt a flash of annoyance, again, at her insistence on being … likable. It's hard to hate a woman who gets excited over an enthusiastically affectionate, not-quite-housebroken mutt, isn't it?

And so Addison got Meredith's dog. And her boyfriend. And her trailer and the healing green woods all around it, and the lake, and…

"How are you feeling back there?"

"Oh, great." Meredith presses a hand to her forehead as the car accelerates jumpily. Maybe it's the heels, but Addison has a lead foot.

"Are you drinking water?"

Meredith glances at the untouched bottle. "I'm drinking water."

"Well, drink more."

Meredith takes a grudging sip. "This is … weird, you know that, right?"

"How is it weird?" She sees Addison trying to catch her eye in the rearview mirror.

"How is it … how _isn't_ it weird. I mean you're basically pimping me out to your husband."

"He's not my husband. And I'm not _pimping you out_!"

"You're kind of pimping her out," Mark says, and Addison makes a wordless sound of outrage.

"Fine, not … pimping," Meredith concedes. "Just … offering me up on a silver platter, fine."

"That doesn't sound so bad." Mark turns in his seat to raise his eyebrows at her suggestively.

"Really? You're going to flirt with me, now, in front of … in front of the trailer," she finishes, because they've started up the long winding drive she still remembers so well.

"He can't help it. It's like breathing for him. Just ignore it. _Mark._ " Addison frees a hand from the wheel to swat him. "Knock it off."

"I can't help it. I'm frustrated."

"Knowing you, it's barely been a day."

"It's been a lot longer than a day with you and that's the only thing that's going to cut it."

If Meredith's not mistaken, Addison actually looks flattered, and when Mark's hand drifts down to her leg Meredith decides her time in the awkwardmobile has come to an end.

"You can just leave me here."

"But…"

"It's fifty feet up. I could use the air." Meredith takes the bottle of water from the backseat. "Um … thanks for the ride."

"Grey." Mark sticks his head out the passenger side. "Walk tall."

"What?"

"Walk tall. You love him. So go tell him. Whatever happens, at least he'll know. You won't have to wonder. So … walk tall, Grey."

She'll have to figure out later if that makes any sense, so for now she just nods and makes her way up the dirt drive.

Ten feet from the trailer, she stops and just … looks at it.

And then she hears barking.

One step onto the porch and she hears a voice, too.

His voice.

"Doc – it's okay, go back to sleep, that's a good boy, it's okay, it's just a squirrel."

Derek is the kind of guy who comforts his dog, she reminds herself. He deserves to know how she feels, if only for that reason.

"Meredith?"

She looks up, surprised. As surprised as he sounds. She didn't see him open the door.

"…hi," she says, for lack of anything better. He looks about as good as Addison did, exhausted as hell with his hair rumpled in that way that she knows means he's been running his hands through it with frustration. He's wearing an old tee shirt and sweatpants, one hand on Doc's happily panting head. And he smells like scotch and there are dark circles under his eyes.

He's perfect.

"What are you doing here?" He looks confused.

"I'm … walking tall?"

His brow furrows. "You're what?"

"Never mind." She shakes her head. "Can I come in?"

"Of course." He opens the door wider. "But it's a mess. I'm a mess," he adds.

He's not wrong. The trailer looks a bit like it's been ransacked, with open cabinets, empty plastic tubs, sheafs of paper … certainly not what she's used to.

"You should see the other guy," Derek jokes weakly.

"I already did. The other guy drove me here."

His eyes widen. "The other…"

"…your wife."

"She's not my wife."

"Derek…"

"Meredith. Addison and I are over."

That was certainly the impression Addison gave her, but she needs to hear it from Derek.

"You've said that before," she reminds him.

He nods toward the kitchen table. "But this time it's official."

She picks up the envelope, slides out a stack of paper. She knows what she'll find, but she wants to see it anyway, and she does.

Two signatures.

Steady, looping signatures with no hint of indecision.

She looks up at him. "You signed."

"We signed." He sits down on the edge of the bed.

"Are you … okay?"

"Yes. No. I'm okay," he says. "I'm … let's just say it's been a long night."

She knows the feeling.

"Addison left," Meredith prompts, looking at the empty space in the cabinets where, no doubt, her crazy shoe collection used to reside.

"Addison left."

Meredith scans his face. He looks … exhausted, like a man who's been through battle. But there's something else in his eyes.

"Are you…"

"It was time," he says. He looks down at his hands for a moment, and when he looks up she recognizes the emotion. It's relief. "She lied to me, about her involvement with Mark."

 _Oh._ Some of what she heard in the bar makes more sense now. But she waits for Derek to continue.

"It wasn't a one-night stand. They lived together, and she didn't tell me until tonight."

"Are you … angry?"

"Angry?" He shakes his head. "No. Maybe I should be, maybe that's part of the … no. I probably should have figured it out, but…" he pauses, looks at her again. "She really drove you here?"

Meredith shrugs. "She was sober."

"She was." Derek nods. "What about …?"

Meredith nods.

"She went back to him." Derek doesn't look surprised, or hurt, more … peaceful.

Meredith nods again. "She went back to him."

"It's good. It's … I should have sent her back to him when she first got here. I chose wrong, Meredith. When I chose her, I chose wrong."

"Maybe you did." She socks her head slightly. Because maybe they actually needed this. To make the wrong choice first, so the right choice would actually make sense.

 _Walk tall, Grey._

"Or maybe it was the right choice at the time, and now … "

She sees hope flicker across his eyes.

"…now we can make a different choice."

"Meredith…"

"And they can ride off into the sunset, and you don't have to feel bad about it."

"I don't feel bad about – the sunset?" He interrupts himself. "Is that what they're doing?"

"Well, they missed the sunset." It's black night outside the trailer, but she knows if they were to walk out onto the porch the sky would light up with more stars than Derek could ever hope to see in Manhattan.

"Derek…"

"Yeah?"

"Screw the sunset."

He laughs, and the sound makes something grow inside her.

"Screw the sunset?"

"Screw the sunset," she confirms. "They can keep the sunset. I'll take the mist rising off the lake in the morning."

"Yeah?"

"It's a beautiful view," she admits.

"It's, um," he looks embarrassed to say it, but finally finishes the sentence, "it's not as beautiful when you're not here."

"Derek…"

"Yeah, I'm a little embarrassed I said that."

"Don't be. It was … nice."

"Nice." He shakes his head. "I didn't think _nice_ was what you were looking for."

"Oh, really?" It's her turn to laugh. "I'm still here, aren't I?"

"You're still here."

"Maybe I'll even be here in the morning, when the mist rises off the lake and that's … better than the sunset."

"Meredith…" his voice is intense suddenly, so intense it scares her a little.

"It's okay," she says before he can finish. "You – your marriage just ended, you don't need to –"

"My marriage ended a long time ago. We just didn't admit it until tonight. Not because of Mark. And not because of you. You both just got … caught in the crossfire."

"Is that all I am? The girl who got caught in the crossfire?"

"Meredith." His voice is soft, almost wondrous. "No."

"You don't have to decide anything now," she adds, because my god, the man just got … _divorced_ tonight.

"You're not just the girl who got caught in the crossfire." He stands up, takes her face in his hands. "I think you might be the love of my life."

"Derek…"

"I know. I'm sorry, it's – I shouldn't put that on you, not after what I did… I'm sorry, Meredith."

"You're sorry you're in love with me?"

"No. I could never be sorry for that." He smiles, a lopsided smile that she thinks she'd never tire of seeing, and his eyes are glistening. "I'm just sorry it's been so hard."

"But … you're divorced."

"I'm divorced. Or – I will be when the lawyers file those papers and take a bunch of our money, but…"

"Are there things left to …"

"To do, to settle? No." He shakes his head. "Our divorce will be like the end of our marriage. No fighting. No … passion. We're done hurting each other. Meredith." He touches her face again. "I've been an idiot."

She tries to school her face so it doesn't read _yeah, you have._ But he seems to know what she's thinking. It's been like this from the very beginning: no wall between them. Like the first time they met they'd already known each other all their lives.

"So just … stop being an idiot then." She smiles at him. "Can you do that?"

"I can try."

"I know it's been a … long night," she says tentatively.

"Yeah," and it comes out like half a rueful laugh. "That's an understatement. And I'm … god, I'm glad you're here, but Meredith … I'm going to need some time. I don't want to hurt you again, I can't hurt you again, and … yeah. Time."

Of course. The ink isn't even dry on the divorce papers.

But there's ink. The divorce papers have ink. And if the divorce papers have ink, then they do have time – they have all the time in the world.

"I understand." She takes a slight step back, because standing this close to him isn't great for her self-control – he has the effect of tequila sometimes, but without the hangover.

Well, sometimes the hangover too. But it's worth it.

And thanks to tequila, she's well acquainted with the cab companies that can manage to drive out to the trailer. She takes a few steps away from him and leans against the small kitchen table, scrolling through her cell phone.

"Meredith – what are you doing?"

"I'm giving you time." She smiles at him. "I'm going to go. It's okay, really, Derek, I understand, it's been a- what are you doing?"

But his fingers have curled into her belt loops and he's tugging her closer. "Derek… you said you needed time."

"I did say that."

"Then why are you…"

He stands up, pulling her flush against him.

"I need time, but I don't need space."

"Derek."

He leans down and silences her with a kiss. It's the first time his lips have touched hers since she cried in the rain outside the hospital, numb from her mother's admittance. That kiss was sad, a little desperate, half- _please_ and half- _goodbye._

This one is completely different.

It's brand new and totally familiar all at once and she feels it everywhere, warmth spreading through her limbs. She hasn't been warm, really _warm,_ since their last night together. His hands frame her face, so gently, and she believes that he doesn't want to hurt her again. There's intensity in the kiss, urgency even, but no desperation.

And then she stops analyzing it because he's lifted her against his body and she's wrapping her legs around him and his hands are tangling in her hair and there's nothing left to think about except the way they fit together.

"Derek, wait."

He stops kissing her and just looks at her - his eyes are hazy with lust, her favorite shade of blue.

"The sheets…"

"Right."

"Sorry." She touches his chest.

"Don't be." He stands up again, setting her on her feet. "A surgeon's first thought should always be sterility. Nice work, Dr. Grey."

Except she can still feel his hands on her, it's burning where he's touched her, and if he's going to stop then she might actually die – so to hell with it, if Addison can screw Mark on Derek's sheets then she can screw Derek on Addison's sheets – it's kind of poetic, isn't it?

"Derek, wait… it's okay…"

But he's already crossed the few steps to the shower and turned it on full blast.

He turns back to her with a smile she recognizes. "It's clean in here," he says.

"It's clean in here," Meredith repeats. She sheds the rest of her clothes, not missing the appreciative look in Derek's eyes. "But I have a feeling we're about to make it dirty. Very, very dirty."

"You think so?"

"Oh, I know so."

"Then get in here."

"Whatever you say, Dr. Shepherd."

…she's still there, in the morning, when the mist rises off the lake.

And the morning after that.

And the morning after – well, you get the idea.

...

"Good morning."

Derek's tone is gentle, wondrous even.

"Good morning," he says again, pausing for a response.

"Derek, she's not going to answer you."

"She might." He grins at her.

"She can't talk yet, you do know that … she's only six hours old."

"But she's very advanced. Didn't you see her APGAR?"

"I did."

"Then you know she's brilliant."

"I know she's brilliant."

His eyes are so soft. Meredith adjusts the warm weight of their daughter's small body, just a little bit, hoping she'll open her eyes again soon so they can see the shade of blue. She swears it's his, and he swears it's hers … the truth (because in every argument there's always his side, her side, and the truth), is probably that it's right in between.

Derek strokes one of her soft little cheeks and Meredith smiles as the tiny rosebud of her mouth purses, ready to suckle.

"She's perfect."

"She's perfect," Meredith agrees.

"How can something so perfect come from something so-"

"Don't say it." She tries to glare at him, but it's too hard; they're not lying about what oxytocin does to you. She feels loopy and happy – positively bright and shiny – and that's saying a lot considering what her body has gone through in the last twenty-four hours.

"What?" Derek looks at her innocently. "I was going to say something nice."

"You were _going_ to say something dirty."

"You think you have me pegged?"

"I know I have you pegged."

"I'm not peggable."

"You're pegged." She tilts her face up so he can kiss her, careful of the baby resting on her chest. "I've had you pegged for a long time. Deal with it."

"Whatever you say, Dr. Grey-Shepherd."

* * *

 _Oh, my god, I wrote MerDer. Please review, don't make a lady beg, because this is scary stuff! I mean, I was originally just going to write their reconciliation in the trailer, and then the gods of fluff reached down from the clouds and forced me to give them a fat happy baby. But seriously, though. MerDer. I might be getting into them. I **might** be super into their marital problems in Season 11 (you know I love marital problems), and Zola's adoption in Season 8. So ... can I handle them?_


End file.
